I think the router is reporting the max speed that it has negotiated with the equipment at the exchange, the speedtest is reporting the actual value available. Your distance from the exhange is only one of many vairables that come into play, though in general the closer the better, it's not the only thing to consider.
One is moving house shortly and broadband is top of my list to get right, more important than the curtains, though the mrs doesn't like hearing me say that. Having done some research into broadband I've come to the conclusion it's all being sold on lies and deception.